Lecture 18: Macroscopic momentum balance for pressure-drop in a tubular flow
From the above expression, one can also determine viscosity of a fluid by measuring pressure- drop across a tube for different flowrates:
(Fig. 18b)
The above-plot is known as pseudo-shear diagram, which is generally used to determine the viscosity of a slurry-mixture. A similar approach can be followed to determine the viscosity or effective viscosity of Non-Newtonian fluids.
Bingham plastic fluid
Such a fluid has the following shear-stress vs strain rate characteristics:
-----------(1)
where is known as the yield stress. Fluid is supposed to be ‘frozen’ if
vs strain rate 
characteristics:
is known as the yield stress. Fluid is supposed to be ‘frozen’ if 
